1. Field of the Invention
The present invention relates to an image processing apparatus and image processing method which calculate indexes associated with the cardiac function of an subject to be examined, more specifically, indexes associated with the blood flow function.
2. Description of the Related Art
In X-ray CT examination, cardiac function analysis is performed. More specifically, blood flow analysis is performed on a left ventricular myocardial region. In blood flow analysis, an ROI (region of interest) (typically a left ventricular myocardial region) as an analysis target is set, and the change amount of contrast medium concentration in the set ROI is calculated. Various indexes associated with hemodynamics are then calculated on the basis of the calculated value. A typical blood flow analysis technique requires the data of the change amount of contrast medium concentration at a plurality of times.
As a technique of setting a myocardial region, the level set method disclosed in, for example, Japanese Patent No. 3902765 is known. According to such a conventional technique, any myocardial region cannot be specified in volume data at a time when no contrast medium is present, because the cardiac muscle is equal in pixel value to the lumen. In volume data with sufficient contrast based on a contrast medium, the contour of the myocardial region is faithfully specified, and an ROI is set to the specified myocardial region. For this reason, owing to the pulsation of the heart or a partial volume effect, the pixel values in the myocardial region are influenced by a contrast medium in a region other than the myocardial region, e.g., the left ventricular lumen and the pixel values in the papillary muscle region, lung region, or the like, and hence the accuracy of blood flow analysis decreases. Furthermore, when a plurality of ROIs are to be set in time-series volume data, since each ROI is set by repeating similar processing for the volume data, the amount of computation becomes enormous.